The discussion in this thread is interesting. Especially when doing a parallel with the new M3/M4 threads where it is all about how the new F8X M3/M4 will be lighter by about 200-300lb. The big argument on the F8X M3/M4 is about how much better it will perform despite it having the same power output as the E9X because of its lighter weight.

The moonroof is 45lb more compared to the CF roof. That is 15-25% of the weight saving the F8X will get over the E9X...

I don't see how they are going to shed 200-300 lb on a slightly larger car. Wishful thinking IMHO.